1. Field of the Invention
This invention related to the processing of nonpetroleum crude oils such as fats, animal and vegetable oils, and more particularly, it relates to an improved process for refining crude oil by a multistep unique treating process.
2. Description of the Prior Art
Many nonpetroleum crude oils (e.g., fats, vegetable and animal oils) are used for human consumption and other utilizations. The crude oil is purified chemically and mechanically to remove solids, to improve chemical properties, color, odor, enhance storage stability and to make a more suitable oil for ultimate utilization. Present day treatment of crude oils consist generally of the steps of refining, hydrogenation, bleaching and deodorization. The term "refining" refers to any purification treatment designed to remove undesirable materials such as free fatty acids, phosphatides, or mucilaginous material, or caustic reactible and acidic impurities in the crude oil.
Most commonly, the refining of the crude oil employs an aqueous alkali, such as sodium hydroxide, to remove the acidic materials and the organic materials capable of undergoing a reaction with the crude oil under controlled reaction conditions so as to induce maximum removal of the acidic and other caustic reactants from the crude oil. Alkali metal soaps and other types of soaplike materials are formed by the caustic reaction with the acidic and other caustic reactants in the crude oil. These caustic reactant materials are in the form of creamlike or mayonnaise-like material with a different soapstock or higher specific gravity as the treated oil. A bulk aqueous phase containing the major portion of the alkali metal soaps is separated from the treated oil. However, the treated oil contains a substantial portion of the alkali metal soaps and the caustic reactant materials. This physical suspension requires an enhanced separation of the alkali metal soaps to a reduced level in the treated oil. Gravity separators, but preferably centrifuges, are employed for this purpose. As a result, the alkali metal soaps content of the treated oil may have been reduced to about 1 percent by weight. Unfortunately, these soaps are most difficult to separate further from the treated oil by physical methods since they are in a finely divided liquid state.
Present day refining practices can use a water-wash for the treated oil to reduce the residual amounts of alkali metal soaps. An intimate mixing of hot water with the treated oil is required followed by bulk phase separation. Then, the water-washed treated oil is subjected to extreme levels of enhanced gravity separation by series flow centrifuges, mechanical filters, or the like. Although the water-wash step does reduce the alkali metal soap content of the treated oil, the refining operator faces four severe problems. A relatively large waste water stream must be processed to recover entrained treated oil which is removed concomitantly with the washing water. Also, the wash water is processed for recovery of the alkali metal salts which create a severe water pollution problem in water handling systems. The wash water increases the free fatty acid content of the treated oil since the water wash and centrifugal separation steps are time domain and cause hydrolysis of neutral oils to occur through their intimate contact with the wash water, especially at elevated temperatures. Needless to say, the refining operator faces costly centrifugal machinery repair and maintenance.
The refinery operator has tried many procedures for avoiding the difficulties existing in the reaction of crude oil with aqueous alkali. Up to the present time, and for the past 80 years, the same basic steps have been employed industry-wise for the reaction of crude oil with aqueous alkali, and the subsequent water-washing of crude oil with oil to reduce the residual content of alkali metal soaps and caustic reactants carried in the treated oil.
The present invention is an improved process for the refining of crude oil wherein the reaction of the crude oil and aqueous alkali may be affected by intimate mixing so that the highest removal of acidic material and caustic reactants occurs without regard to subsequent phase separation procedures. More particularly, this improved process avoids the necessity of water-washing and the expensive centrifugal separation steps heretofore practised in the refinery art. An additional advantage resides in the present improved process wherein residual alkali metal soaps, irrespective of particle size and liquid phase conditions, are substantially removed from a treated oil. This novel process produces a purified oil of high purity with a greatly reduced content of alkali metal soaps. An important advantage in the improved process is the removal of finely divided solid material, such as clays, rust, etc., during the removal of alkali metal soaps. Furthermore, the alkali metal soaps can be recovered separately from these finely divided solid materials.